New Delhi – Relief supplies continued flowing into Burma, but international aid agencies could not reach the hardest-hit areas because of massive logistical problems.

"We have not distributed yet to the worst-hit area of Irrawaddy division," said James East, spokesman for World Vision. "Because of transportation, it's difficult to get aid to the areas. This is a major challenge now. The delta areas all the way have poor roads, and flooding. Roads are blocked and bridges are collapsed."

The cyclone slammed into the Irrawaddy Delta and Rangoon on Friday and Saturday, claiming more than 50,000 lives. Vast areas of the delta were reportedly still under water, with decomposing corpses of humans and animals still uncollected.

The death toll is expected to rise as tens of thousands are still missing and up to one million are homeless and in desperate need of food and supplies.

Other agencies face similar challenges delivering aid, but most have been able to reach areas near Rangoon to distribute rice, blankets, water purification tablets and plastic sheeting for tents.

Paul Risley, regional information officer for the World Food Programme said, "Probably the Irrawaddy division has the hardest-hit areas and now we are trying to start supplying aid to those areas, but it's very difficult."

WFP began distributing some of the 800 tonnes of rice in its Rangoon warehouse after receiving permission from the Burmese government yesterday. World Vision began distributing its aid the day after the storm.

UNICEF has emergency supplies for 155,000 people and is trying to get the aid out as quickly as possible. A UNICEF assessment team reported that some areas are "very hard affected," according to Shantha Bloeman, agency spokesperson from Thailand.

The UN's humanitarian chief, John Holmes, said 24 countries had pledged more than $30 million in aid to the relief effort and that a WFP plane loaded with 45 tonnes of high-energy biscuits arrived in Rangoon on Wednesday.

"It's clear here we're faced with a major catastrophe," he said, while reading Secretary-General Ban Ki-moon's statement that it is "critical to get aid in as quickly as possible." An international flash appeal will be issued worldwide on Friday, Holmes said.

World Vision assessment teams went out today and will assess five of the worst-hit areas in the delta to draw up distribution and assistance plans. The assessment team will see how many people are affected, according to James. "We want to help 50,000 people within 30 days," he said.

The UN and other agencies said they were still having problems obtaining visas to get international staff into Burma.

"We have a plan to send emergency staff on standby to help," Bloeman said. "They haven't yet got visas from the Burmese government, but we are hoping to become clear in the next few days."

East said, "I think some people are getting in, but I am just not quite sure what's happening to the other aid agencies at the movement."

The UN's Holmes said the agency was "making some progress" with Burmese authorities in getting visas for staff.

Meanwhile, aid agencies stressed the need to coordinate the relief effort.

"We have very, very important, good coordination responses in different UN agencies. Aid groups coordinate with the government to make sure we reach those people," Bloeman said.

The United States, meanwhile, has pledged $3.25 million to cyclone victims. "Let the United States come to help you, help the people," President George W. Bush said. "We want to help them deal with this terrible disaster."